I know definition is hard job, expecially I) verbal definition, which must find the essence (nature, substance,...) of an entity (being: [ object, thing..], [concept, idea, category...]), and needs interdisciplinary help from ontology, linguistics (morpho-syntax, semantics), logic and epistemology..... but I do hope a phisicist could explain why Quantity of Motion ? just two questions: 1) why motion? it doesnt seem a technical (precise,defined...) term, I never found it elsewhere. Is it different from movement, speed ,velocity v ? I know v is a vector, speed is not. But motion? 2) Why add quantity? is "quantity of motion" a different category from motion is "quantity of energy", (books,pears...) different from energy (...) II) numeric definition : p = m * v (mass-by-velocity) seems simpler (just arithmetics) and more precise, effective, decisive, conclusive... But please read the following with care, it is not a joke but a very profound issue 1) we have ...... ......... 10 (sweets) and 5 (children), let's multiply : ........ 10 * 5 = 50 (fifty what? I say: children, and I am not joking) someone says: NO WAY! it's sweets.He is using commonsense and (probably) he's right, but can he disprove me with scientific foolproof arguments? 2) Now we have 10 (crates) and 5 (boxes) , we get 50 what? 3)are we allowed to create a new category just by multiplication?... so we'd have sweet-by-child, crate-by-box, jam-by-jar ... ad lib ?